It is frequently desirable to measure the acoustic impedance of a material. The acoustic impedance gives information as to how much of an incoming sound wave is reflected and how much is absorbed. Thus, the acoustic impedance gives an indication of the sound-absorbing properties of the material.
Further, measurement of the acoustic impedance can give an indirect indication as to the structural properties of the material. For example, if the material includes a honeycomb laminated to a smooth outer sheet, a different acoustic impedance will be measured if the bonds between the honeycomb and the sheet are properly made as compared with the case of improperly formed bonds.
The measurement of acoustic impedance frequently requires that a slug of the material in question be cut from the material and inserted into what is called an acoustic impedance tube. Such cutting of course damages the material, thus perhaps rendering the cut region unusable. Therefore, this measurement procedure allows one to only make assumptions about the acoustic impedance of materials which have been manufactured under conditions similar to those of the cut material. One such material can be material in regions adjacent to the cut material. Another such material can be contained in an article manufactured in the same production batch as the cut material.